Atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G) are associated with dysregulation and overactivation of the complement alternative pathway. Typically, gene analysis for aHUS and C3G is undertaken in small patient numbers, yet it is unclear which genes most frequently predispose to aHUS or C3G. Accordingly, we performed a six-center analysis of 610 rare genetic variants in 13 mostly complement genes (, ,, ,, ,, ,, ,, , and) from >3500 patients with aHUS and C3G. We report 371 novel rare variants (RVs) for aHUS and 82 for C3G. Our new interactive Database of Complement Gene Variants was used to extract allele frequency data for these 13 genes using the Exome Aggregation Consortium server as the reference genome. For aHUS, significantly more protein-altering rare variation was found in five genes ,, ,, and than in the Exome Aggregation Consortium (allele frequency< 0.01%), thus correlating these with aHUS. For C3G, an association was only found for RVs in and the N-terminal C3b-binding or C-terminal nonsurface-associated regions of In conclusion, the RV analyses showed nonrandom distributions over the affected proteins, and different distributions were observed between aHUS and C3G that clarify their phenotypes.

Post-infectious glomerulonephritis is a common disorder that develops following an infection. In the majority of cases, there is complete recovery of renal function within a few days to weeks following resolution of the infection. In a small percentage of patients, however, the glomerulonephritis takes longer to resolve resulting in persistent hematuria and proteinuria, or even progression to end-stage kidney disease. In some cases of persistent hematuria and proteinuria, kidney biopsies show findings of a post-infectious glomerulonephritis even in the absence of any evidence of a preceding infection. The cause of such ‘atypical’ post-infectious glomerulonephritis, with or without evidence of preceding infection, is unknown. Here, we show that most patients diagnosed with this ‘atypical’ post-infectious glomerulonephritis have an underlying defect in the regulation of the alternative pathway of complement. These defects include mutations in complement regulating proteins and antibodies to the C3 convertase known as C3 nephritic factors. As a result, the activated alternative pathway is not brought under control even after resolution of the infection. Hence, the sequela is continual glomerular deposition of complement factors with resultant inflammation and development of an ‘atypical’ post-infectious glomerulonephritis.

Although the diagnosis of Gitelman syndrome (GS) and Bartter syndrome (BS) is now feasible by genetic analysis, implementation of genetic testing for these disorders is still hampered by several difficulties, including large gene dimensions, lack of hot-spot mutations, heavy workup time, and costs. This study evaluated in a cohort of patients with genetically proven GS or BS diagnostic sensibility and specificity of a diuretic test with oral hydrochlorothiazide (HCT test). Forty-one patients with GS (22 adults, aged 25 to 57; 19 children-adolescents, aged 7 to 17) and seven patients with BS (five type I, two type III) were studied; three patients with "pseudo-BS" from surreptitious diuretic intake (two patients) or vomiting (one patient) were also included. HCT test consisted of the administration of 50 mg of HCT orally (1 mg/kg in children-adolescents) and measurement of the maximal diuretic-induced increase over basal in the subsequent 3 h of chloride fractional clearance. All but three patients with GS but no patients with BS and pseudo-BS showed blunted (<2.3%) response to HCT; patients with BS and the two patients with pseudo-BS from diuretic intake had increased response to HCT. No overlap existed between patients with GS and both patients with BS and pseudo-BS. The response to HCT test is blunted in patients with GS but not in patients with BS or nongenetic hypokalemia. In patients with the highly selected phenotype of normotensive hypokalemic alkalosis, abnormal HCT test allows prediction with a very high sensitivity and specificity of the Gitelman genotype and may avoid genotyping. M utations of several genes that are involved in Na/ fluid reabsorption along the distal nephron are the cause of tubular disorders that are characterized by chronic hypokalemic alkalosis and normotensive, hyperreninemic hyperaldosteronism, including Gitelman syndrome (GS; OMIM 263800) and Bartter syndrome (BS) types I to V (1-3) (OMIM 241200, 601678, 607364, 602522, and 601199). Chronic normotensive hypokalemia and alkalosis may also be acquired as a result of known or unknown diuretic use, anorexia/bulimia, and laxative abuse (4 -6). Clinical history and biochemical workup may not allow definite diagnosis, especially concerning the different types of tubular disorders. Genetic diagnosis is now feasible for all known genes that are responsible for GS and BS, but in everyday practice, it remains not easily available for the clinician and, for the geneticist, costly, cumbersome, and time-consuming as a result of the great dimension of most genes, lack of hot-spot mutations, and the very large number of mutations described. Furthermore, in approximately 40% of patients with GS, only a single heterozygous mutation in the SLC12A3 gene is detected (7), so further examination of a second gene is usually necessary.Tests with diuretics have been used in the past to diagnose tubular disorders (8 -12) and nontubular conditions (5); however, genetic confirmation of the supposed diagnosis was rarely, if ever, available. We present the di...

Background and objectives C3 glomerulopathy (C3G) applies to a group of renal diseases defined by a specific renal biopsy finding: a dominant pattern of C3 fragment deposition on immunofluorescence. The primary pathogenic mechanism involves abnormal control of the alternative complement pathway, although a full description of the disease spectrum remains to be determined. This study sought to validate and define the association of complement dysregulation with C3G and to determine whether specific complement pathway abnormalities could inform disease definition.Design, setting, participants, & measurements This study included 34 patients with C3G (17 with C3 glomerulonephritis [C3GN] and 17 with dense deposit disease [DDD]) diagnosed between 2008 and 2013 selected from the C3G Registry. Control samples (n=100) were recruited from regional blood drives. Nineteen complement biomarkers were assayed on all samples. Results were compared between C3G disease categories and with normal controls.Results Assessment of the alternative complement pathway showed that compared with controls, patients with C3G had lower levels of serum C3 (P,0.001 for both DDD and C3GN) and factor B (P,0.001 for both DDD and C3GN) as well as higher levels of complement breakdown products including C3d (P,0.001 for both DDD and C3GN) and Bb (P,0.001 for both DDD and C3GN). A comparison of terminal complement pathway proteins showed that although C5 levels were significantly suppressed (P,0.001 for both DDD and C3GN) its breakdown product C5a was significantly higher only in patients with C3GN (P,0.05). Of the other terminal pathway components (C6-C9), the only significant difference was in C7 levels between patients with C3GN and controls (P,0.01). Soluble C5b-9 was elevated in both diseases but only the difference between patients with C3GN and controls reached statistical significance (P,0.001). Levels of C3 nephritic factor activity were qualitatively higher in patients with DDD compared with patients with C3GN.Conclusions Complement biomarkers are significantly abnormal in patients with C3G compared with controls. These data substantiate the link between complement dysregulation and C3G and identify C3G interdisease differences.

The thrombotic microangiopathies (TMAs) and C3 glomerulopathies (C3Gs) include a spectrum of rare diseases such as atypical hemolytic uremic syndrome, thrombotic thrombocytopenic purpura, C3GN, and dense deposit disease, which share phenotypic similarities and underlying genetic commonalities. Variants in several genes contribute to the pathogenesis of these diseases, and identification of these variants may inform the diagnosis and treatment of affected patients. We have developed and validated a comprehensive genetic panel that screens all exons of all genes implicated in TMA and C3G. The closely integrated pipeline implemented includes targeted genomic enrichment, massively parallel sequencing, bioinformatic analysis, and a multidisciplinary conference to analyze identified variants in the context of each patient's specific phenotype. Herein, we present our 1-year experience with this panel, during which time we studied 193 patients. We identified 17 novel and 74 rare variants, which we classified as pathogenic (11), likely pathogenic (12), and of uncertain significance (68). Compared with controls, patients with C3G had a higher frequency of rare and novel variants in C3 convertase (C3 and CFB) and complement regulator (CFH, CFI, CFHR5, and CD46) genes (P,0.05). In contrast, patients with TMA had an increase in rare and novel variants only in complement regulator genes (P,0.01), a distinction consistent with differing sites of complement dysregulation in these two diseases. In summary, we were able to provide a positive genetic diagnosis in 43% and 41% of patients carrying the clinical diagnosis of C3G and TMA, respectively.

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Patients with Bartter syndrome type I and II tend to present a satisfactory prognosis after a median follow-up of more than 10 years. Gallstones might represent a new complication of antenatal Bartter syndrome.

C3 glomerulopathy (C3G) is an ultra-rare complement-mediated renal disease characterized histologically by the predominance of C3 deposition within in the glomerulus. Familial cases of C3G are extremely uncommon and offer unique insight into the genetic drivers of complement dysregulation. In this report, we describe a patient who presented with C3G. Because a relative carried the same diagnosis, we sought an underlying genetic commonality to explain the phenotype. As part of a comprehension genetic screen, we completed multiplex ligation-dependent probe amplification across the complement factor H related region and identified amplification alterations consistent with a genomic rearrangement. Using comparative genomic hybridization, we narrowed and then cloned the rearrangement breakpoints thereby defining a novel fusion gene that is translated into a serum protein comprised of factor H related-5 (short consensus repeats 1 and 2) and factor H-related-2 (short consensus repeats 1-4). These data highlight the role of factor H related proteins in the control of complement activity and illustrate how perturbation of that control leads to C3G.